Bloom is essentially a "random", but small spread of the bullets. When you shoot a bullet (at least right now), it does not go directly forward where you shoot. It goes a bit high, bit low, a bit left, etc. This means that even if you are aiming with the crosshair directly on the opponent, there is a chance that it may miss. Sorry if my explanation is not great but hopefully this helps!

I recommend trying my loadout, it's nice. If you stay on the assault rifle, you can switch to shotgun or the 3rd slot. I put the more rare items in my last slot because I don't like when there's a slot with nothing in it lmao